Gantz tells the story of Kei Kurono and his friend Masaru Kato who die in a train accident and become part of a semi-posthumous "game" in which they and several other recently deceased people are forced to hunt down and kill aliens armed with a handful of futuristic items of equipment and weaponry.
the story really is unique, i mean people who die get ressurected by a big black ball to kill aliens? AWESOME
Hearing the thoughts of the main character is also lots of fun since he's a real meanie and a perv (watch ep1 and u will know what i mean) lol. Beware! the ending differs from the manga, in the manga the story is still ongoing. You should defenitly try this anime out.